$ git clone -n https://src.fedoraproject.org/rpms/genimage.git /var/lib/mock/f42-build-61027213-6587875/root/chroot_tmpdir/scmroot/genimage
Cloning into '/var/lib/mock/f42-build-61027213-6587875/root/chroot_tmpdir/scmroot/genimage'...
$ git fetch origin 26ce5d10c1834895be596012c69e040810488da7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/genimage
 * [new ref]         26ce5d10c1834895be596012c69e040810488da7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 26ce5d1 Update to 19 release